According to the state of the art, automatic transmissions, particularly for motor vehicles, comprise planetary gear sets, which are shifted using friction and/or shifting elements, such as clutches and brakes, and which are typically connected to a starting element that is subject to a slip effect and optionally provided with a converter lock-up clutch, for example a hydrodynamic torque converter or a fluid clutch.
A transmission of this type is described in EP 0 434 525 A1. It basically includes an input shaft and an output shaft, which are arranged parallel to each other, a double planetary gear set arranged concentrically in relation to the output shaft, and five control elements in the form of three clutches and two brakes, the selective operation of which in pairs determines the different gear ratios between the input shaft and the output shaft. This transmission has a front-mounted gear set and two power paths, so that by the selective engagement in pairs of the five control elements, six forward gears are obtained.
In the first power path, two clutches are required for transmitting the torque from the front-mounted gear set to two elements of the double planetary gear set. These elements are arranged in the power flow direction substantially downstream of the front-mounted gear set in the direction of the double planetary gear set. A further clutch is provided in the second power path which detachably connects this path to a further element of the double-ratio planetary gear set. The clutches are arranged such that the inner disk carrier forms the output end.
Furthermore, from the published prior art U.S. Pat. No. 6,139,463 a compact multi-speed transmission in planetary design, particularly for a motor vehicle is known, which has two planetary gear sets and one front-mounted gear set as well as three clutches and two brakes. In this known multi-speed transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting the torque from the front-mounted gear set to the two planetary gear sets. The outer disk carrier and/or the cylinder or piston and pressure compensation side of the clutch C-3 are connected to a first brake B-1. Furthermore, the inner disk carrier of the third clutch C-3 is connected to the cylinder and/or piston and pressure compensation sides of the first clutch C-1, the inner disk carrier of the first clutch C-1 being arranged on the output side and connected to a sun gear of the third planetary gear set.
A multi-speed transmission is also known from DE 199 49 507 A1 by the applicant, according to which on the drive shaft two non-shiftable, front-mounted gear sets are provided, which on the output side generate two rotational speeds which, in addition to the rotational speed of the input shaft, can be selectively switched by engaging the control elements to a shiftable double planetary gear set acting upon the output shaft such that, for changing from one gear to the next higher or lower gear of the two actuated control elements, only one control element must be engaged or disengaged.
DE 199 12 480 A1 discloses an automatically shiftable motor vehicle transmission with three planet carrier-mounted planetary gear sets as well as three brakes and two clutches for switching between six forward gears and one reverse gear and with one drive shaft and one output shaft. The automatically shiftable motor vehicle transmission is configured such that the drive shaft is directly connected to the sun gear of the second planetary gear set and that the drive shaft can be connected, via the first clutch, to the sun gear of the first planetary gear set and/or, via the second clutch, to the planet carrier of the first planetary gear set. In addition, or as an alternative, the sun gear of the first planetary gear set can be connected, via the first brake, to the housing of the transmission and/or the planet carrier of the first planetary gear set can be connected, via the second brake, to the housing and/or the sun gear of the third planetary gear set, via the third brake, to the housing.
Furthermore, DE 102 13 820 A1 discloses a multi-speed automatic transmission, comprising a first input path T1 of a first transmission ratio, an input path T2, which has a larger transmission ratio than the input path T1, a planetary gear set of four elements, wherein the four elements are a first element, a second element, a third element, and a fourth element following an order of elements on a speed diagram, a clutch C-2 transmitting rotation from the input path T2 to the first element S3, a clutch C-1 transmitting the rotation from the input path T2 to the fourth element S2, a clutch C-4 transmitting rotation from the input path T1 to the first element, a clutch C-3 transmitting the rotation from the input path T1 to the second element C3, a brake B-1 engaging the fourth element, a brake B-2 engaging the second element, and an output member coupled to the third element R3.
A multi-speed transmission is described within the framework of DE 101 15 983 A1 by the applicant, comprising a drive shaft that is linked to a front-mounted gear set, an output shaft that is connected to a rear-mounted gear set, and a maximum of seven shifting elements, through the selective shifting of which at least seven forward gears can be shifted without range shifting. The front-mounted gear set is formed by a front-mounted planetary gear set or a maximum of two non-shiftable front-mounted planetary gear sets linked to the first front-mounted planetary gear set, wherein the rear-mounted gear set is configured as a two-planet carrier four-shaft transmission with two shiftable rear-mounted planetary gear sets and has four free shafts. The first free shaft of this two-planet carrier four-shaft transmission is connected to the first shifting element, the second free shaft to the second and third shifting elements, the third free shaft to the fourth and fifth shifting elements and the fourth free shaft is connected to the output shaft. According to the invention, a multi-speed transmission with a total of six shifting elements is proposed, which connects the third free shaft or the first free shaft of the rear-mounted gear set additionally to a sixth shifting element. For a multi-speed transmission with a total of seven control elements, it is proposed according to the invention that the third free shaft is additionally connected to a sixth control element D′ and the first free shaft additionally to a seventh control element.
A multi-speed transmission with at least seven gears is described within the framework of DE 101 15 987. In addition to the input shaft and the output shaft, this transmission comprises a non-shiftable front-mounted gear set and shiftable rear-mounted gear set in the form of a two-carrier four-shaft transmission. The front-mounted gear set comprises a first planetary gear set, which in addition to the input rotational speed of the input shaft also provides a second rotational speed, which may optionally be shifted to the rear-mounted gear set. The rear-mounted gear set comprises two engageable planetary gear sets, which can shift at least seven gears using the six shift elements, forming two power paths. Here during each shifting operation, advantageously range shifting is avoided. A 9-gear multi-speed transmission is furthermore known from DE 29 36 969; it comprises eight shift elements and four gear sets.
Automatic motor vehicle transmissions in planetary design in general have previously been described in the state of the art on many occasions and are subject to continuous refinements and improvements. These transmissions should have low complexity, in particular require a small number of shifting elements, and avoid double-shifts when shifting sequentially, so that always only one shifting element is engaged when shifting in defined gear groups.
Previously planetary transmissions generally only had one reverse gear, however planetary transmissions are also known to have additional reverse gears, which can either be shifted using the existing shifting elements in the planetary transmission, or are implemented by means of an additional reverse gear set. The disadvantage with the known planetary transmissions is accordingly either the insufficient number and insufficient gear ratios of the reverse gears or the constructional expenditure required for realizing the reverse gears.